diff --git a/docs/src/reference/models.md b/docs/src/reference/models.md
index 76f9a9154b..7efc192469 100644
--- a/docs/src/reference/models.md
+++ b/docs/src/reference/models.md
@@ -18,6 +18,7 @@ get
 get!
 set
 supports
+attribute_value_type
 ```
 
 ## Model interface
diff --git a/docs/src/tutorials/implementing.md b/docs/src/tutorials/implementing.md
index f8e54d68be..432a12be0e 100644
--- a/docs/src/tutorials/implementing.md
+++ b/docs/src/tutorials/implementing.md
@@ -271,6 +271,11 @@ For each attribute
  * [`supports`](@ref) returns a `Bool` indicating whether the solver supports the
    attribute.
 
+!!! info
+    Use [`attribute_value_type`](@ref) to check the value expected by a given
+    attribute. You should make sure that your [`get`](@ref) function correctly
+    infers to this type (or a subtype of it).
+
 Each column in the table indicates whether you need to implement the particular
 method for each attribute.
 
diff --git a/src/Bridges/Constraint/bridge.jl b/src/Bridges/Constraint/bridge.jl
index 5e97bbd3c0..3e17de7b69 100644
--- a/src/Bridges/Constraint/bridge.jl
+++ b/src/Bridges/Constraint/bridge.jl
@@ -27,10 +27,10 @@ function bridge_constraint end
 
 The number of variables created by the bridge `b` in the model.
 """
-MOI.get(::AbstractBridge, ::MOI.NumberOfVariables) = 0
+MOI.get(::AbstractBridge, ::MOI.NumberOfVariables)::Int64 = 0
 
 """
-    MOI.get(b::AbstractBridge, ::MOI.NumberOfVariables)
+    MOI.get(b::AbstractBridge, ::MOI.ListOfVariableIndices)
 
 The list of variables created by the bridge `b` in the model.
 """
diff --git a/src/Bridges/Constraint/det.jl b/src/Bridges/Constraint/det.jl
index e8073392f5..b0a5521391 100644
--- a/src/Bridges/Constraint/det.jl
+++ b/src/Bridges/Constraint/det.jl
@@ -210,7 +210,10 @@ function subsum(
 end
 
 # Attributes, Bridge acting as a model
-MOI.get(b::LogDetBridge, ::MOI.NumberOfVariables) = length(b.Δ) + length(b.l)
+
+function MOI.get(b::LogDetBridge, ::MOI.NumberOfVariables)::Int64
+    return length(b.Δ) + length(b.l)
+end
 
 MOI.get(b::LogDetBridge, ::MOI.ListOfVariableIndices) = [b.Δ; b.l]
 
@@ -220,21 +223,21 @@ function MOI.get(
         MOI.VectorAffineFunction{T},
         MOI.PositiveSemidefiniteConeTriangle,
     },
-) where {T}
+)::Int64 where {T}
     return 1
 end
 
 function MOI.get(
     b::LogDetBridge{T},
     ::MOI.NumberOfConstraints{MOI.VectorAffineFunction{T},MOI.ExponentialCone},
-) where {T}
+)::Int64 where {T}
     return length(b.lcindex)
 end
 
 function MOI.get(
     ::LogDetBridge{T},
     ::MOI.NumberOfConstraints{MOI.ScalarAffineFunction{T},MOI.LessThan{T}},
-) where {T}
+)::Int64 where {T}
     return 1
 end
 
@@ -407,7 +410,8 @@ function MOIB.added_constraint_types(::Type{RootDetBridge{T}}) where {T}
 end
 
 # Attributes, Bridge acting as a model
-MOI.get(b::RootDetBridge, ::MOI.NumberOfVariables) = length(b.Δ)
+
+MOI.get(b::RootDetBridge, ::MOI.NumberOfVariables)::Int64 = length(b.Δ)
 
 MOI.get(b::RootDetBridge, ::MOI.ListOfVariableIndices) = copy(b.Δ)
 
@@ -417,7 +421,7 @@ function MOI.get(
         MOI.VectorAffineFunction{T},
         MOI.PositiveSemidefiniteConeTriangle,
     },
-) where {T}
+)::Int64 where {T}
     return 1
 end
 
@@ -427,7 +431,7 @@ function MOI.get(
         MOI.VectorAffineFunction{T},
         MOI.GeometricMeanCone,
     },
-) where {T}
+)::Int64 where {T}
     return 1
 end
 
diff --git a/src/Bridges/Constraint/functionize.jl b/src/Bridges/Constraint/functionize.jl
index 956dd05dc3..f78e1b42e0 100644
--- a/src/Bridges/Constraint/functionize.jl
+++ b/src/Bridges/Constraint/functionize.jl
@@ -54,7 +54,7 @@ end
 function MOI.get(
     ::ScalarFunctionizeBridge{T,S},
     ::MOI.NumberOfConstraints{MOI.ScalarAffineFunction{T},S},
-) where {T,S}
+)::Int64 where {T,S}
     return 1
 end
 
@@ -158,7 +158,7 @@ end
 function MOI.get(
     ::VectorFunctionizeBridge{T,S},
     ::MOI.NumberOfConstraints{MOI.VectorAffineFunction{T},S},
-) where {T,S}
+)::Int64 where {T,S}
     return 1
 end
 
diff --git a/src/Bridges/Constraint/geomean.jl b/src/Bridges/Constraint/geomean.jl
index 8efc89c21c..d8229baf5c 100644
--- a/src/Bridges/Constraint/geomean.jl
+++ b/src/Bridges/Constraint/geomean.jl
@@ -164,29 +164,29 @@ function concrete_bridge_type(
 end
 
 # Attributes, Bridge acting as a model
-MOI.get(b::GeoMeanBridge, ::MOI.NumberOfVariables) = length(b.xij)
+MOI.get(b::GeoMeanBridge, ::MOI.NumberOfVariables)::Int64 = length(b.xij)
 
 MOI.get(b::GeoMeanBridge, ::MOI.ListOfVariableIndices) = copy(b.xij)
 
 function MOI.get(
     ::GeoMeanBridge{T,F},
     ::MOI.NumberOfConstraints{F,MOI.LessThan{T}},
-) where {T,F}
+)::Int64 where {T,F}
     return 1 # t ≤ x_{l1}/sqrt(N)
 end
 
 function MOI.get(
     b::GeoMeanBridge{T,F,G},
     ::MOI.NumberOfConstraints{G,MOI.RotatedSecondOrderCone},
-) where {T,F,G}
+)::Int64 where {T,F,G}
     return length(b.socrc)
 end
 
 function MOI.get(
     b::GeoMeanBridge{T,F,G},
     ::MOI.NumberOfConstraints{G,MOI.Nonnegatives},
-) where {T,F,G}
-    return (b.d > 2 ? 0 : 1)
+)::Int64 where {T,F,G}
+    return b.d > 2 ? 0 : 1
 end
 
 function MOI.get(
diff --git a/src/Bridges/Constraint/geomean_to_relentr.jl b/src/Bridges/Constraint/geomean_to_relentr.jl
index fd60647810..e25696ca2b 100644
--- a/src/Bridges/Constraint/geomean_to_relentr.jl
+++ b/src/Bridges/Constraint/geomean_to_relentr.jl
@@ -86,7 +86,7 @@ function concrete_bridge_type(
 end
 
 # Attributes, Bridge acting as a model
-MOI.get(bridge::GeoMeantoRelEntrBridge, ::MOI.NumberOfVariables) = 1
+MOI.get(::GeoMeantoRelEntrBridge, ::MOI.NumberOfVariables)::Int64 = 1
 
 function MOI.get(bridge::GeoMeantoRelEntrBridge, ::MOI.ListOfVariableIndices)
     return [bridge.y]
@@ -95,14 +95,14 @@ end
 function MOI.get(
     ::GeoMeantoRelEntrBridge{T,F},
     ::MOI.NumberOfConstraints{F,MOI.Nonnegatives},
-) where {T,F}
+)::Int64 where {T,F}
     return 1
 end
 
 function MOI.get(
     ::GeoMeantoRelEntrBridge{T,F,G},
     ::MOI.NumberOfConstraints{G,MOI.RelativeEntropyCone},
-) where {T,F,G}
+)::Int64 where {T,F,G}
     return 1
 end
 
diff --git a/src/Bridges/Constraint/indicator_sos.jl b/src/Bridges/Constraint/indicator_sos.jl
index 528b1619b0..8e921fb660 100644
--- a/src/Bridges/Constraint/indicator_sos.jl
+++ b/src/Bridges/Constraint/indicator_sos.jl
@@ -154,9 +154,7 @@ end
 
 # Attributes, Bridge acting as a model
 
-function MOI.get(::IndicatorSOS1Bridge, ::MOI.NumberOfVariables)
-    return 1
-end
+MOI.get(::IndicatorSOS1Bridge, ::MOI.NumberOfVariables)::Int64 = 1
 
 function MOI.get(b::IndicatorSOS1Bridge, ::MOI.ListOfVariableIndices)
     return [b.w_variable]
@@ -165,28 +163,28 @@ end
 function MOI.get(
     ::IndicatorSOS1Bridge{T,BC,Nothing},
     ::MOI.NumberOfConstraints{MOI.SingleVariable,BC},
-) where {T,BC}
+)::Int64 where {T,BC}
     return 0
 end
 
 function MOI.get(
     ::IndicatorSOS1Bridge{T,BC,CI},
     ::MOI.NumberOfConstraints{MOI.SingleVariable,BC},
-) where {T,BC,CI<:MOI.ConstraintIndex{MOI.SingleVariable,BC}}
+)::Int64 where {T,BC,CI<:MOI.ConstraintIndex{MOI.SingleVariable,BC}}
     return 1
 end
 
 function MOI.get(
     ::IndicatorSOS1Bridge,
     ::MOI.NumberOfConstraints{MOI.VectorOfVariables,<:MOI.SOS1},
-)
+)::Int64
     return 1
 end
 
 function MOI.get(
     ::IndicatorSOS1Bridge{T,BC},
     ::MOI.NumberOfConstraints{MOI.ScalarAffineFunction{T},BC},
-) where {T,BC,CI<:MOI.ConstraintIndex{MOI.SingleVariable,BC}}
+)::Int64 where {T,BC,CI<:MOI.ConstraintIndex{MOI.SingleVariable,BC}}
     return 1
 end
 
diff --git a/src/Bridges/Constraint/interval.jl b/src/Bridges/Constraint/interval.jl
index 89a3f736fb..47ea728a5a 100644
--- a/src/Bridges/Constraint/interval.jl
+++ b/src/Bridges/Constraint/interval.jl
@@ -86,14 +86,14 @@ end
 function MOI.get(
     ::SplitIntervalBridge{T,F,S,LS},
     ::MOI.NumberOfConstraints{F,LS},
-) where {T,F,S,LS}
+)::Int64 where {T,F,S,LS}
     return 1
 end
 
 function MOI.get(
     ::SplitIntervalBridge{T,F,S,LS,US},
     ::MOI.NumberOfConstraints{F,US},
-) where {T,F,S,LS,US}
+)::Int64 where {T,F,S,LS,US}
     return 1
 end
 
diff --git a/src/Bridges/Constraint/norm_spec_nuc_to_psd.jl b/src/Bridges/Constraint/norm_spec_nuc_to_psd.jl
index 8c083e34cf..be3a8764fd 100644
--- a/src/Bridges/Constraint/norm_spec_nuc_to_psd.jl
+++ b/src/Bridges/Constraint/norm_spec_nuc_to_psd.jl
@@ -70,9 +70,9 @@ end
 
 # Attributes, Bridge acting as a model
 function MOI.get(
-    bridge::NormSpectralBridge{T,F,G},
+    ::NormSpectralBridge{T,F,G},
     ::MOI.NumberOfConstraints{F,MOI.PositiveSemidefiniteConeTriangle},
-) where {T,F,G}
+)::Int64 where {T,F,G}
     return 1
 end
 
@@ -282,7 +282,7 @@ function concrete_bridge_type(
 end
 
 # Attributes, Bridge acting as a model
-function MOI.get(bridge::NormNuclearBridge, ::MOI.NumberOfVariables)
+function MOI.get(bridge::NormNuclearBridge, ::MOI.NumberOfVariables)::Int64
     return length(bridge.U) + length(bridge.V)
 end
 
@@ -291,16 +291,16 @@ function MOI.get(bridge::NormNuclearBridge, ::MOI.ListOfVariableIndices)
 end
 
 function MOI.get(
-    bridge::NormNuclearBridge{T,F,G,H},
+    ::NormNuclearBridge{T,F,G,H},
     ::MOI.NumberOfConstraints{F,MOI.GreaterThan{T}},
-) where {T,F,G,H}
+)::Int64 where {T,F,G,H}
     return 1
 end
 
 function MOI.get(
-    bridge::NormNuclearBridge{T,F,G,H},
+    ::NormNuclearBridge{T,F,G,H},
     ::MOI.NumberOfConstraints{G,MOI.PositiveSemidefiniteConeTriangle},
-) where {T,F,G,H}
+)::Int64 where {T,F,G,H}
     return 1
 end
 
diff --git a/src/Bridges/Constraint/norm_to_lp.jl b/src/Bridges/Constraint/norm_to_lp.jl
index 4c24ab99c9..8f856ce3b6 100644
--- a/src/Bridges/Constraint/norm_to_lp.jl
+++ b/src/Bridges/Constraint/norm_to_lp.jl
@@ -150,12 +150,14 @@ function concrete_bridge_type(
 end
 
 # Attributes, Bridge acting as a model
-MOI.get(b::NormOneBridge, ::MOI.NumberOfVariables) = length(b.y)
+MOI.get(b::NormOneBridge, ::MOI.NumberOfVariables)::Int64 = length(b.y)
+
 MOI.get(b::NormOneBridge, ::MOI.ListOfVariableIndices) = copy(b.y)
+
 function MOI.get(
-    b::NormOneBridge{T,F},
+    ::NormOneBridge{T,F},
     ::MOI.NumberOfConstraints{F,MOI.Nonnegatives},
-) where {T,F}
+)::Int64 where {T,F}
     return 1
 end
 
diff --git a/src/Bridges/Constraint/quad_to_soc.jl b/src/Bridges/Constraint/quad_to_soc.jl
index fe61be5ea6..1bef004e07 100644
--- a/src/Bridges/Constraint/quad_to_soc.jl
+++ b/src/Bridges/Constraint/quad_to_soc.jl
@@ -189,7 +189,7 @@ function MOI.get(
         MOI.VectorAffineFunction{T},
         MOI.RotatedSecondOrderCone,
     },
-) where {T}
+)::Int64 where {T}
     return 1
 end
 
diff --git a/src/Bridges/Constraint/relentr_to_exp.jl b/src/Bridges/Constraint/relentr_to_exp.jl
index f2176038c9..f52e7fb328 100644
--- a/src/Bridges/Constraint/relentr_to_exp.jl
+++ b/src/Bridges/Constraint/relentr_to_exp.jl
@@ -82,7 +82,7 @@ function concrete_bridge_type(
 end
 
 # Attributes, Bridge acting as a model
-function MOI.get(bridge::RelativeEntropyBridge, ::MOI.NumberOfVariables)
+function MOI.get(bridge::RelativeEntropyBridge, ::MOI.NumberOfVariables)::Int64
     return length(bridge.y)
 end
 
@@ -91,16 +91,16 @@ function MOI.get(bridge::RelativeEntropyBridge, ::MOI.ListOfVariableIndices)
 end
 
 function MOI.get(
-    bridge::RelativeEntropyBridge{T,F},
+    ::RelativeEntropyBridge{T,F},
     ::MOI.NumberOfConstraints{F,MOI.GreaterThan{T}},
-) where {T,F}
+)::Int64 where {T,F}
     return 1
 end
 
 function MOI.get(
     bridge::RelativeEntropyBridge{T,F,G},
     ::MOI.NumberOfConstraints{G,MOI.ExponentialCone},
-) where {T,F,G}
+)::Int64 where {T,F,G}
     return length(bridge.y)
 end
 
diff --git a/src/Bridges/Constraint/scalarize.jl b/src/Bridges/Constraint/scalarize.jl
index 22aae28a3c..2bc1f7632e 100644
--- a/src/Bridges/Constraint/scalarize.jl
+++ b/src/Bridges/Constraint/scalarize.jl
@@ -58,7 +58,7 @@ end
 function MOI.get(
     bridge::ScalarizeBridge{T,F,S},
     ::MOI.NumberOfConstraints{F,S},
-) where {T,F,S}
+)::Int64 where {T,F,S}
     return length(bridge.scalar_constraints)
 end
 
diff --git a/src/Bridges/Constraint/semi_to_binary.jl b/src/Bridges/Constraint/semi_to_binary.jl
index d7997a28f6..f51ddabe30 100644
--- a/src/Bridges/Constraint/semi_to_binary.jl
+++ b/src/Bridges/Constraint/semi_to_binary.jl
@@ -214,9 +214,7 @@ end
 
 # Attributes, Bridge acting as a model
 
-function MOI.get(::SemiToBinaryBridge, ::MOI.NumberOfVariables)
-    return 1
-end
+MOI.get(::SemiToBinaryBridge, ::MOI.NumberOfVariables)::Int64 = 1
 
 function MOI.get(b::SemiToBinaryBridge, ::MOI.ListOfVariableIndices)
     return [b.binary_variable]
@@ -225,28 +223,28 @@ end
 function MOI.get(
     ::SemiToBinaryBridge{T,S},
     ::MOI.NumberOfConstraints{MOI.SingleVariable,MOI.ZeroOne},
-) where {T,S}
+)::Int64 where {T,S}
     return 1
 end
 
 function MOI.get(
     ::SemiToBinaryBridge{T,S},
     ::MOI.NumberOfConstraints{MOI.SingleVariable,MOI.Integer},
-) where {T,S<:MOI.Semiinteger}
+)::Int64 where {T,S<:MOI.Semiinteger}
     return 1
 end
 
 function MOI.get(
     ::SemiToBinaryBridge{T,S},
     ::MOI.NumberOfConstraints{MOI.ScalarAffineFunction{T},MOI.GreaterThan{T}},
-) where {T,S}
+)::Int64 where {T,S}
     return 1
 end
 
 function MOI.get(
     ::SemiToBinaryBridge{T,S},
     ::MOI.NumberOfConstraints{MOI.ScalarAffineFunction{T},MOI.LessThan{T}},
-) where {T,S}
+)::Int64 where {T,S}
     return 1
 end
 
diff --git a/src/Bridges/Constraint/set_map.jl b/src/Bridges/Constraint/set_map.jl
index d023223d34..ce090d4e3a 100644
--- a/src/Bridges/Constraint/set_map.jl
+++ b/src/Bridges/Constraint/set_map.jl
@@ -64,7 +64,7 @@ end
 function MOI.get(
     ::SetMapBridge{T,S2,S1,F},
     ::MOI.NumberOfConstraints{F,S2},
-) where {T,S2,S1,F}
+)::Int64 where {T,S2,S1,F}
     return 1
 end
 
diff --git a/src/Bridges/Constraint/slack.jl b/src/Bridges/Constraint/slack.jl
index 12433d5905..730625601c 100644
--- a/src/Bridges/Constraint/slack.jl
+++ b/src/Bridges/Constraint/slack.jl
@@ -15,14 +15,14 @@ end
 function MOI.get(
     ::AbstractSlackBridge{T,VF,ZS,F},
     ::MOI.NumberOfConstraints{F,ZS},
-) where {T,VF,ZS,F}
+)::Int64 where {T,VF,ZS,F}
     return 1
 end
 
 function MOI.get(
     ::AbstractSlackBridge{T,VF,ZS,F,S},
     ::MOI.NumberOfConstraints{VF,S},
-) where {T,VF,ZS,F,S}
+)::Int64 where {T,VF,ZS,F,S}
     return 1
 end
 
@@ -217,7 +217,7 @@ function concrete_bridge_type(
 end
 
 # Attributes, Bridge acting as a model
-MOI.get(b::ScalarSlackBridge, ::MOI.NumberOfVariables) = 1
+MOI.get(b::ScalarSlackBridge, ::MOI.NumberOfVariables)::Int64 = 1
 MOI.get(b::ScalarSlackBridge, ::MOI.ListOfVariableIndices) = [b.slack]
 
 # Attributes, Bridge acting as a constraint
@@ -332,7 +332,8 @@ function concrete_bridge_type(
 end
 
 # Attributes, Bridge acting as a model
-MOI.get(b::VectorSlackBridge, ::MOI.NumberOfVariables) = length(b.slack)
+MOI.get(b::VectorSlackBridge, ::MOI.NumberOfVariables)::Int64 = length(b.slack)
+
 MOI.get(b::VectorSlackBridge, ::MOI.ListOfVariableIndices) = copy(b.slack)
 
 # Attributes, Bridge acting as a constraint
diff --git a/src/Bridges/Constraint/soc_to_nonconvex_quad.jl b/src/Bridges/Constraint/soc_to_nonconvex_quad.jl
index e58832f39b..be3c0a9d53 100644
--- a/src/Bridges/Constraint/soc_to_nonconvex_quad.jl
+++ b/src/Bridges/Constraint/soc_to_nonconvex_quad.jl
@@ -172,7 +172,7 @@ end
 function MOI.get(
     ::AbstractSOCtoNonConvexQuadBridge{T},
     ::MOI.NumberOfConstraints{MOI.ScalarQuadraticFunction{T},MOI.LessThan{T}},
-) where {T}
+)::Int64 where {T}
     return 1
 end
 
@@ -189,7 +189,7 @@ end
 function MOI.get(
     bridge::AbstractSOCtoNonConvexQuadBridge{T},
     ::MOI.NumberOfConstraints{MOI.ScalarAffineFunction{T},MOI.GreaterThan{T}},
-) where {T}
+)::Int64 where {T}
     return length(bridge.var_pos)
 end
 
diff --git a/src/Bridges/Constraint/square.jl b/src/Bridges/Constraint/square.jl
index 4604d9963c..2f80b7ea11 100644
--- a/src/Bridges/Constraint/square.jl
+++ b/src/Bridges/Constraint/square.jl
@@ -167,14 +167,14 @@ end
 function MOI.get(
     ::SquareBridge{T,F,G,TT},
     ::MOI.NumberOfConstraints{F,TT},
-) where {T,F,G,TT}
+)::Int64 where {T,F,G,TT}
     return 1
 end
 
 function MOI.get(
     bridge::SquareBridge{T,F,G},
     ::MOI.NumberOfConstraints{G,MOI.EqualTo{T}},
-) where {T,F,G}
+)::Int64 where {T,F,G}
     return length(bridge.sym)
 end
 
diff --git a/src/Bridges/Constraint/vectorize.jl b/src/Bridges/Constraint/vectorize.jl
index 8baf067467..0ec7f28449 100644
--- a/src/Bridges/Constraint/vectorize.jl
+++ b/src/Bridges/Constraint/vectorize.jl
@@ -74,7 +74,7 @@ end
 function MOI.get(
     ::VectorizeBridge{T,F,S},
     ::MOI.NumberOfConstraints{F,S},
-) where {T,F,S}
+)::Int64 where {T,F,S}
     return 1
 end
 
diff --git a/src/Bridges/Constraint/zero_one.jl b/src/Bridges/Constraint/zero_one.jl
index d7677b2356..230dc69dcb 100644
--- a/src/Bridges/Constraint/zero_one.jl
+++ b/src/Bridges/Constraint/zero_one.jl
@@ -101,16 +101,16 @@ end
 
 # Attributes, Bridge acting as a model
 function MOI.get(
-    bridge::ZeroOneBridge{T},
+    ::ZeroOneBridge{T},
     ::MOI.NumberOfConstraints{MOI.SingleVariable,MOI.Interval{T}},
-) where {T}
+)::Int64 where {T}
     return 1
 end
 
 function MOI.get(
-    bridge::ZeroOneBridge,
+    ::ZeroOneBridge,
     ::MOI.NumberOfConstraints{MOI.SingleVariable,MOI.Integer},
-)
+)::Int64
     return 1
 end
 
diff --git a/src/Bridges/Objective/functionize.jl b/src/Bridges/Objective/functionize.jl
index 1e0590d19f..2d5e705861 100644
--- a/src/Bridges/Objective/functionize.jl
+++ b/src/Bridges/Objective/functionize.jl
@@ -38,9 +38,7 @@ function MOIB.set_objective_function_type(
 end
 
 # Attributes, Bridge acting as a model
-function MOI.get(::FunctionizeBridge, ::MOI.NumberOfVariables)
-    return 0
-end
+MOI.get(::FunctionizeBridge, ::MOI.NumberOfVariables)::Int64 = 0
 
 function MOI.get(::FunctionizeBridge, ::MOI.ListOfVariableIndices)
     return MOI.VariableIndex[]
diff --git a/src/Bridges/Objective/slack.jl b/src/Bridges/Objective/slack.jl
index 33259bdfc2..a47af4b502 100644
--- a/src/Bridges/Objective/slack.jl
+++ b/src/Bridges/Objective/slack.jl
@@ -78,9 +78,7 @@ function concrete_bridge_type(
 end
 
 # Attributes, Bridge acting as a model
-function MOI.get(::SlackBridge, ::MOI.NumberOfVariables)
-    return 1
-end
+MOI.get(::SlackBridge, ::MOI.NumberOfVariables)::Int64 = 1
 
 function MOI.get(bridge::SlackBridge, ::MOI.ListOfVariableIndices)
     return [bridge.slack]
@@ -89,7 +87,7 @@ end
 function MOI.get(
     bridge::SlackBridge{T,F},
     ::MOI.NumberOfConstraints{F,S},
-) where {T,F,S<:Union{MOI.GreaterThan{T},MOI.LessThan{T}}}
+)::Int64 where {T,F,S<:Union{MOI.GreaterThan{T},MOI.LessThan{T}}}
     return bridge.constraint isa MOI.ConstraintIndex{F,S} ? 1 : 0
 end
 
diff --git a/src/Bridges/Variable/free.jl b/src/Bridges/Variable/free.jl
index e96e39d608..33569a016d 100644
--- a/src/Bridges/Variable/free.jl
+++ b/src/Bridges/Variable/free.jl
@@ -34,7 +34,7 @@ function MOIB.added_constraint_types(::Type{FreeBridge{T}}) where {T}
 end
 
 # Attributes, Bridge acting as a model
-function MOI.get(bridge::FreeBridge, ::MOI.NumberOfVariables)
+function MOI.get(bridge::FreeBridge, ::MOI.NumberOfVariables)::Int64
     return length(bridge.variables)
 end
 
@@ -45,7 +45,7 @@ end
 function MOI.get(
     ::FreeBridge,
     ::MOI.NumberOfConstraints{MOI.VectorOfVariables,MOI.Nonnegatives},
-)
+)::Int64
     return 1
 end
 
diff --git a/src/Bridges/Variable/rsoc_to_psd.jl b/src/Bridges/Variable/rsoc_to_psd.jl
index 8825c2960c..cc1646cab8 100644
--- a/src/Bridges/Variable/rsoc_to_psd.jl
+++ b/src/Bridges/Variable/rsoc_to_psd.jl
@@ -89,7 +89,7 @@ function MOIB.added_constraint_types(::Type{RSOCtoPSDBridge{T}}) where {T}
 end
 
 # Attributes, Bridge acting as a model
-function MOI.get(bridge::RSOCtoPSDBridge, ::MOI.NumberOfVariables)
+function MOI.get(bridge::RSOCtoPSDBridge, ::MOI.NumberOfVariables)::Int64
     return length(bridge.variables)
 end
 
@@ -100,8 +100,12 @@ end
 function MOI.get(
     bridge::RSOCtoPSDBridge,
     ::MOI.NumberOfConstraints{MOI.VectorOfVariables,S},
-) where {S<:Union{MOI.PositiveSemidefiniteConeTriangle,MOI.Nonnegatives}}
-    return bridge.psd isa MOI.ConstraintIndex{MOI.VectorOfVariables,S} ? 1 : 0
+)::Int64 where {S<:Union{MOI.PositiveSemidefiniteConeTriangle,MOI.Nonnegatives}}
+    if bridge.psd isa MOI.ConstraintIndex{MOI.VectorOfVariables,S}
+        return 1
+    else
+        return 0
+    end
 end
 
 function MOI.get(
@@ -118,7 +122,7 @@ end
 function MOI.get(
     bridge::RSOCtoPSDBridge{T},
     ::MOI.NumberOfConstraints{MOI.SingleVariable,MOI.EqualTo{T}},
-) where {T}
+)::Int64 where {T}
     return length(bridge.off_diag)
 end
 
@@ -132,7 +136,7 @@ end
 function MOI.get(
     bridge::RSOCtoPSDBridge{T},
     ::MOI.NumberOfConstraints{MOI.ScalarAffineFunction{T},MOI.EqualTo{T}},
-) where {T}
+)::Int64 where {T}
     return length(bridge.diag)
 end
 
diff --git a/src/Bridges/Variable/set_map.jl b/src/Bridges/Variable/set_map.jl
index 0f86f7fa96..38896a632d 100644
--- a/src/Bridges/Variable/set_map.jl
+++ b/src/Bridges/Variable/set_map.jl
@@ -59,7 +59,7 @@ function MOIB.added_constraint_types(::Type{<:SetMapBridge})
 end
 
 # Attributes, Bridge acting as a model
-function MOI.get(bridge::SetMapBridge, ::MOI.NumberOfVariables)
+function MOI.get(bridge::SetMapBridge, ::MOI.NumberOfVariables)::Int64
     return length(bridge.variables)
 end
 
@@ -70,14 +70,14 @@ end
 function MOI.get(
     ::SetMapBridge{T,S1},
     ::MOI.NumberOfConstraints{MOI.SingleVariable,S1},
-) where {T,S1<:MOI.AbstractScalarSet}
+)::Int64 where {T,S1<:MOI.AbstractScalarSet}
     return 1
 end
 
 function MOI.get(
     ::SetMapBridge{T,S1},
     ::MOI.NumberOfConstraints{MOI.VectorOfVariables,S1},
-) where {T,S1<:MOI.AbstractVectorSet}
+)::Int64 where {T,S1<:MOI.AbstractVectorSet}
     return 1
 end
 
diff --git a/src/Bridges/Variable/vectorize.jl b/src/Bridges/Variable/vectorize.jl
index 91bc403a73..5fad63075f 100644
--- a/src/Bridges/Variable/vectorize.jl
+++ b/src/Bridges/Variable/vectorize.jl
@@ -48,9 +48,7 @@ function concrete_bridge_type(
 end
 
 # Attributes, Bridge acting as a model
-function MOI.get(::VectorizeBridge, ::MOI.NumberOfVariables)
-    return 1
-end
+MOI.get(::VectorizeBridge, ::MOI.NumberOfVariables)::Int64 = 1
 
 function MOI.get(bridge::VectorizeBridge, ::MOI.ListOfVariableIndices)
     return [bridge.variable]
@@ -59,7 +57,7 @@ end
 function MOI.get(
     ::VectorizeBridge{T,S},
     ::MOI.NumberOfConstraints{MOI.VectorOfVariables,S},
-) where {T,S}
+)::Int64 where {T,S}
     return 1
 end
 
diff --git a/src/Bridges/Variable/zeros.jl b/src/Bridges/Variable/zeros.jl
index 381fa3e2cc..63d1b6aff3 100644
--- a/src/Bridges/Variable/zeros.jl
+++ b/src/Bridges/Variable/zeros.jl
@@ -40,7 +40,7 @@ function MOIB.added_constraint_types(::Type{<:ZerosBridge})
 end
 
 # Attributes, Bridge acting as a model
-MOI.get(bridge::ZerosBridge, ::MOI.NumberOfVariables) = 0
+MOI.get(::ZerosBridge, ::MOI.NumberOfVariables)::Int64 = 0
 
 function MOI.get(bridge::ZerosBridge, ::MOI.ListOfVariableIndices)
     return MOI.VariableIndex[]
diff --git a/src/Bridges/bridge.jl b/src/Bridges/bridge.jl
index 7c185aef95..8b84e530a3 100644
--- a/src/Bridges/bridge.jl
+++ b/src/Bridges/bridge.jl
@@ -34,7 +34,7 @@ end
 The number of constraints of the type `F`-in-`S` created by the bridge `b` in
 the model.
 """
-MOI.get(::AbstractBridge, ::MOI.NumberOfConstraints) = 0
+MOI.get(::AbstractBridge, ::MOI.NumberOfConstraints)::Int64 = 0
 
 """
     MOI.get(b::AbstractBridge, ::MOI.ListOfConstraintIndices{F, S}) where {F, S}
diff --git a/src/Bridges/bridge_optimizer.jl b/src/Bridges/bridge_optimizer.jl
index 9be95eefec..7da990a94b 100644
--- a/src/Bridges/bridge_optimizer.jl
+++ b/src/Bridges/bridge_optimizer.jl
@@ -726,7 +726,7 @@ function MOI.get(
     return list
 end
 
-function MOI.get(b::AbstractBridgeOptimizer, attr::MOI.NumberOfVariables)
+function MOI.get(b::AbstractBridgeOptimizer, attr::MOI.NumberOfVariables)::Int64
     s =
         MOI.get(b.model, attr) +
         Variable.number_of_variables(Variable.bridges(b))
@@ -765,7 +765,7 @@ end
 function MOI.get(
     b::AbstractBridgeOptimizer,
     attr::MOI.NumberOfConstraints{F,S},
-) where {F,S}
+)::Int64 where {F,S}
     s = get_all_including_bridged(b, attr)
     # The constraints counted in `s` may have been added by bridges
     for bridge in values(Variable.bridges(b))
diff --git a/src/DeprecatedTest/modellike.jl b/src/DeprecatedTest/modellike.jl
index f617171bcb..dd5d50337b 100644
--- a/src/DeprecatedTest/modellike.jl
+++ b/src/DeprecatedTest/modellike.jl
@@ -401,7 +401,7 @@ abstract type BadModel <: MOI.ModelLike end
 function MOI.get(::BadModel, ::MOI.ListOfModelAttributesSet)
     return MOI.AbstractModelAttribute[]
 end
-MOI.get(::BadModel, ::MOI.NumberOfVariables) = 1
+MOI.get(::BadModel, ::MOI.NumberOfVariables)::Int64 = 1
 MOI.get(::BadModel, ::MOI.ListOfVariableIndices) = [MOI.VariableIndex(1)]
 function MOI.get(::BadModel, ::MOI.ListOfVariableAttributesSet)
     return MOI.AbstractVariableAttribute[]
diff --git a/src/Test/Test.jl b/src/Test/Test.jl
index f2e3a9e046..622071b2df 100644
--- a/src/Test/Test.jl
+++ b/src/Test/Test.jl
@@ -387,6 +387,60 @@ function _test_model_solution(
     return
 end
 
+# TODO(odow): The following are helper functions for testing the value types of
+#     different attributes. The following attributes are not tested:
+# BarrierIterations()
+# CallbackNodeStatus()
+# ConflictStatus()
+# ConstraintBridgingCost()
+# ConstraintConflictStatus()
+# LazyConstraintCallback()
+# NodeCount
+# RelativeGap
+# SimplexIterations
+# VariableBridgingCost()
+
+function _test_attribute_value_type(
+    model::MOI.ModelLike,
+    attribute::Union{MOI.AbstractModelAttribute,MOI.AbstractOptimizerAttribute},
+)
+    T = MOI.attribute_value_type(attribute)
+    @static if VERSION < v"1.5"
+        @test MOI.get(model, attribute) isa T
+    else
+        @test @inferred(T, MOI.get(model, attribute)) isa T
+    end
+    return
+end
+
+function _test_attribute_value_type(
+    model::MOI.ModelLike,
+    attribute::MOI.AbstractConstraintAttribute,
+    ci::MOI.ConstraintIndex,
+)
+    T = MOI.attribute_value_type(attribute)
+    @static if VERSION < v"1.5"
+        @test MOI.get(model, attribute, ci) isa T
+    else
+        @test @inferred(T, MOI.get(model, attribute, ci)) isa T
+    end
+    return
+end
+
+function _test_attribute_value_type(
+    model::MOI.ModelLike,
+    attribute::MOI.AbstractVariableAttribute,
+    x::MOI.VariableIndex,
+)
+    T = MOI.attribute_value_type(attribute)
+    @static if VERSION < v"1.5"
+        @test MOI.get(model, attribute, x) isa T
+    else
+        @test @inferred(T, MOI.get(model, attribute, x)) isa T
+    end
+    return
+end
+
 ###
 ### Include all the test files!
 ###
diff --git a/src/Test/test_attribute.jl b/src/Test/test_attribute.jl
index 93cae893cc..bf9cf3afd1 100644
--- a/src/Test/test_attribute.jl
+++ b/src/Test/test_attribute.jl
@@ -14,6 +14,7 @@ function test_attribute_NumberThreads(model::MOI.AbstractOptimizer, ::Config)
     @test MOI.get(model, MOI.NumberOfThreads()) == 3
     MOI.set(model, MOI.NumberOfThreads(), value)
     @test value == MOI.get(model, MOI.NumberOfThreads())
+    _test_attribute_value_type(model, MOI.NumberOfThreads())
     return
 end
 test_attribute_NumberThreads(::MOI.ModelLike, ::Config) = nothing
@@ -41,7 +42,7 @@ function test_attribute_RawStatusString(
     @requires _supports(config, MOI.RawStatusString)
     MOI.add_variable(model)
     MOI.optimize!(model)
-    @test MOI.get(model, MOI.RawStatusString()) isa AbstractString
+    _test_attribute_value_type(model, MOI.RawStatusString())
     return
 end
 test_attribute_RawStatusString(::MOI.ModelLike, ::Config) = nothing
@@ -80,6 +81,7 @@ function test_attribute_Silent(model::MOI.AbstractOptimizer, ::Config)
     @test !value == MOI.get(model, MOI.Silent())
     MOI.set(model, MOI.Silent(), value)
     @test value == MOI.get(model, MOI.Silent())
+    _test_attribute_value_type(model, MOI.Silent())
     return
 end
 test_attribute_Silent(::MOI.ModelLike, ::Config) = nothing
@@ -100,7 +102,7 @@ Test that the [`MOI.SolverName`](@ref) attribute is implemented for `model`.
 """
 function test_attribute_SolverName(model::MOI.AbstractOptimizer, config::Config)
     if _supports(config, MOI.SolverName)
-        @test MOI.get(model, MOI.SolverName()) isa AbstractString
+        _test_attribute_value_type(model, MOI.SolverName())
     end
     return
 end
@@ -120,6 +122,7 @@ function test_attribute_SolveTimeSec(
     MOI.add_variable(model)
     MOI.optimize!(model)
     @test MOI.get(model, MOI.SolveTimeSec()) >= 0.0
+    _test_attribute_value_type(model, MOI.SolveTimeSec())
     return
 end
 test_attribute_SolveTimeSec(::MOI.ModelLike, ::Config) = nothing
@@ -151,6 +154,7 @@ function test_attribute_TimeLimitSec(model::MOI.AbstractOptimizer, ::Config)
     @test MOI.get(model, MOI.TimeLimitSec()) == 1.0
     MOI.set(model, MOI.TimeLimitSec(), value)
     @test value == MOI.get(model, MOI.TimeLimitSec()) # Equality should hold
+    _test_attribute_value_type(model, MOI.TimeLimitSec())
     return
 end
 test_attribute_TimeLimitSec(::MOI.ModelLike, ::Config) = nothing
diff --git a/src/Test/test_basic_constraint.jl b/src/Test/test_basic_constraint.jl
index 9bab161480..241ec7965f 100644
--- a/src/Test/test_basic_constraint.jl
+++ b/src/Test/test_basic_constraint.jl
@@ -135,6 +135,7 @@ function _basic_constraint_test_helper(
     @test MOI.get(model, MOI.NumberOfConstraints{F,S}()) == 0
     c = MOI.add_constraint(model, constraint_function, set)
     @test MOI.get(model, MOI.NumberOfConstraints{F,S}()) == 1
+    _test_attribute_value_type(model, MOI.NumberOfConstraints{F,S}())
     ###
     ### Test MOI.is_valid
     ###
@@ -157,6 +158,7 @@ function _basic_constraint_test_helper(
             @test MOI.supports(model, MOI.ConstraintName(), typeof(c))
             MOI.set(model, MOI.ConstraintName(), c, "c")
             @test MOI.get(model, MOI.ConstraintName(), c) == "c"
+            _test_attribute_value_type(model, MOI.ConstraintName(), c)
         end
     end
     ###
@@ -166,12 +168,15 @@ function _basic_constraint_test_helper(
         @test MOI.get(model, MOI.ConstraintFunction(), c) ≈ constraint_function
         @test MOI.get(model, MOI.CanonicalConstraintFunction(), c) ≈
               constraint_function
+        _test_attribute_value_type(model, MOI.ConstraintFunction(), c)
+        _test_attribute_value_type(model, MOI.CanonicalConstraintFunction(), c)
     end
     ###
     ### Test MOI.ConstraintSet
     ###
     if _supports(config, MOI.ConstraintSet)
         @test MOI.get(model, MOI.ConstraintSet(), c) == set
+        _test_attribute_value_type(model, MOI.ConstraintSet(), c)
     end
     ###
     ### Test MOI.ListOfConstraintIndices
diff --git a/src/Test/test_linear.jl b/src/Test/test_linear.jl
index f71ea70f27..d1f62edeab 100644
--- a/src/Test/test_linear.jl
+++ b/src/Test/test_linear.jl
@@ -640,6 +640,8 @@ function test_linear_integration_2(
             @test MOI.get(model, MOI.VariableBasisStatus(), y) ==
                   MOI.NONBASIC_AT_LOWER
             @test MOI.get(model, MOI.ConstraintBasisStatus(), c) == MOI.NONBASIC
+            _test_attribute_value_type(model, MOI.ConstraintBasisStatus(), c)
+            _test_attribute_value_type(model, MOI.VariableBasisStatus(), x)
         end
     end
 end
diff --git a/src/Test/test_model.jl b/src/Test/test_model.jl
index 62d8cea500..e1334c1be2 100644
--- a/src/Test/test_model.jl
+++ b/src/Test/test_model.jl
@@ -139,6 +139,7 @@ Test that the default ObjectiveSense is FEASIBILITY_SENSE.
 """
 function test_model_default_ObjectiveSense(model::MOI.ModelLike, ::Config)
     MOI.get(model, MOI.ObjectiveSense()) == MOI.FEASIBILITY_SENSE
+    _test_attribute_value_type(model, MOI.ObjectiveSense())
     return
 end
 
@@ -152,6 +153,7 @@ function test_model_default_TerminationStatus(
     ::Config,
 )
     MOI.get(model, MOI.TerminationStatus()) == MOI.OPTIMIZE_NOT_CALLED
+    _test_attribute_value_type(model, MOI.TerminationStatus())
     return
 end
 
@@ -164,6 +166,7 @@ Test that the default PrimalStatus is NO_SOLUTION.
 """
 function test_model_default_PrimalStatus(model::MOI.AbstractOptimizer, ::Config)
     MOI.get(model, MOI.PrimalStatus()) == MOI.NO_SOLUTION
+    _test_attribute_value_type(model, MOI.PrimalStatus())
     return
 end
 
@@ -176,6 +179,7 @@ Test that the default DualStatus is NO_SOLUTION.
 """
 function test_model_default_DualStatus(model::MOI.AbstractOptimizer, ::Config)
     MOI.get(model, MOI.DualStatus()) == MOI.NO_SOLUTION
+    _test_attribute_value_type(model, MOI.DualStatus())
     return
 end
 
@@ -198,6 +202,7 @@ function test_model_VariableName(model::MOI.ModelLike, ::Config)
     @test MOI.get(model, MOI.VariableIndex, "x1") == x[2]
     MOI.set(model, MOI.VariableName(), x[1], "x1")
     @test_throws ErrorException MOI.get(model, MOI.VariableIndex, "x1")
+    _test_attribute_value_type(model, MOI.VariableName(), x[1])
     return
 end
 
@@ -265,6 +270,7 @@ function test_model_Name(model::MOI.ModelLike, ::Config)
     MOI.set(model, MOI.Name(), "Name2")
     @test MOI.Name() in MOI.get(model, MOI.ListOfModelAttributesSet())
     @test MOI.get(model, MOI.Name()) == "Name2"
+    _test_attribute_value_type(model, MOI.Name())
     return
 end
 
diff --git a/src/Test/test_objective.jl b/src/Test/test_objective.jl
index 674d2087de..fd22b1303d 100644
--- a/src/Test/test_objective.jl
+++ b/src/Test/test_objective.jl
@@ -73,6 +73,8 @@ function test_objective_get_ObjectiveFunction_ScalarAffineFunction(
         MOI.ObjectiveFunction{MOI.ScalarQuadraticFunction{Float64}}(),
     )
     @test convert(MOI.ScalarAffineFunction{Float64}, quad_obj_fun) ≈ f
+    _test_attribute_value_type(model, MOI.ObjectiveFunctionType())
+    _test_attribute_value_type(model, obj_attr)
     return
 end
 
@@ -188,6 +190,11 @@ function test_objective_ObjectiveFunction_SingleVariable(
     )
     MOI.set(model, MOI.ObjectiveSense(), MOI.MIN_SENSE)
     c = MOI.add_constraint(model, MOI.SingleVariable(x), MOI.GreaterThan(1.0))
+    _test_attribute_value_type(model, MOI.ObjectiveFunctionType())
+    _test_attribute_value_type(
+        model,
+        MOI.ObjectiveFunction{MOI.SingleVariable}(),
+    )
     _test_model_solution(
         model,
         config;
diff --git a/src/Test/test_solve.jl b/src/Test/test_solve.jl
index 99b47f5c64..b9c6acac2c 100644
--- a/src/Test/test_solve.jl
+++ b/src/Test/test_solve.jl
@@ -332,7 +332,7 @@ end
 """
     test_solve_result_index(model::MOI.ModelLike, config::Config)
 
-Test that various attributess implement `.result_index` correctly.
+Test that various attributes implement `.result_index` correctly.
 """
 function test_solve_result_index(model::MOI.ModelLike, config::Config)
     @requires _supports(config, MOI.optimize!)
@@ -348,6 +348,7 @@ function test_solve_result_index(model::MOI.ModelLike, config::Config)
     )
     MOI.optimize!(model)
     result_count = MOI.get(model, MOI.ResultCount())
+    _test_attribute_value_type(model, MOI.ResultCount())
     function result_err(attr)
         return MOI.ResultIndexBoundsError{typeof(attr)}(attr, result_count)
     end
diff --git a/src/Test/test_variable.jl b/src/Test/test_variable.jl
index 43bcc236e7..7bff4366ad 100644
--- a/src/Test/test_variable.jl
+++ b/src/Test/test_variable.jl
@@ -7,6 +7,7 @@ function test_variable_add_variable(model::MOI.ModelLike, ::Config)
     @test MOI.get(model, MOI.NumberOfVariables()) == 0
     v = MOI.add_variable(model)
     @test MOI.get(model, MOI.NumberOfVariables()) == 1
+    _test_attribute_value_type(model, MOI.NumberOfVariables())
     return
 end
 
diff --git a/src/Utilities/cachingoptimizer.jl b/src/Utilities/cachingoptimizer.jl
index 495c5905ba..b9844c61db 100644
--- a/src/Utilities/cachingoptimizer.jl
+++ b/src/Utilities/cachingoptimizer.jl
@@ -807,7 +807,7 @@ function MOI.get(model::CachingOptimizer, attr::MOI.AbstractModelAttribute)
         end
         return map_indices(
             model.optimizer_to_model_map,
-            MOI.get(model.optimizer, attr),
+            MOI.get(model.optimizer, attr)::MOI.attribute_value_type(attr),
         )
     else
         return MOI.get(model.model_cache, attr)
@@ -848,7 +848,11 @@ function MOI.get(
         end
         return map_indices(
             model.optimizer_to_model_map,
-            MOI.get(model.optimizer, attr, model.model_to_optimizer_map[index]),
+            MOI.get(
+                model.optimizer,
+                attr,
+                model.model_to_optimizer_map[index],
+            )::MOI.attribute_value_type(attr),
         )
     else
         return MOI.get(model.model_cache, attr, index)
@@ -872,7 +876,7 @@ function MOI.get(
                 model.optimizer,
                 attr,
                 map(index -> model.model_to_optimizer_map[index], indices),
-            ),
+            )::Vector{<:MOI.attribute_value_type(attr)},
         )
     else
         return MOI.get(model.model_cache, attr, indices)
@@ -941,7 +945,7 @@ function MOI.get(model::CachingOptimizer, attr::MOI.AbstractOptimizerAttribute)
     end
     return map_indices(
         model.optimizer_to_model_map,
-        MOI.get(model.optimizer, attr),
+        MOI.get(model.optimizer, attr)::MOI.attribute_value_type(attr),
     )
 end
 
@@ -984,7 +988,7 @@ function MOI.get(
     @assert m.state == ATTACHED_OPTIMIZER
     return map_indices(
         m.optimizer_to_model_map,
-        MOI.get(m.optimizer, attr.attr),
+        MOI.get(m.optimizer, attr.attr)::MOI.attribute_value_type(attr.attr),
     )
 end
 
@@ -998,7 +1002,11 @@ function MOI.get(
     @assert m.state == ATTACHED_OPTIMIZER
     return map_indices(
         m.optimizer_to_model_map,
-        MOI.get(m.optimizer, attr.attr, m.model_to_optimizer_map[idx]),
+        MOI.get(
+            m.optimizer,
+            attr.attr,
+            m.model_to_optimizer_map[idx],
+        )::MOI.attribute_value_type(attr.attr),
     )
 end
 
@@ -1016,7 +1024,7 @@ function MOI.get(
             m.optimizer,
             attr.attr,
             getindex.(m.model_to_optimizer_map, idx),
-        ),
+        )::Vector{<:MOI.attribute_value_type(attr.attr)},
     )
 end
 
diff --git a/src/Utilities/functions.jl b/src/Utilities/functions.jl
index 16095898fa..9dc87b2103 100644
--- a/src/Utilities/functions.jl
+++ b/src/Utilities/functions.jl
@@ -63,7 +63,7 @@ function eval_term(varval::Function, t::MOI.ScalarQuadraticTerm)
 end
 
 """
-    map_indices(index_map::Function, x)
+    map_indices(index_map::Function, x::X)::X where {X}
 
 Substitute any [`MOI.VariableIndex`](@ref) (resp. [`MOI.ConstraintIndex`](@ref))
 in `x` by the [`MOI.VariableIndex`](@ref) (resp. [`MOI.ConstraintIndex`](@ref))
@@ -77,11 +77,17 @@ submittable value.
 function map_indices end
 
 """
-    map_indices(variable_map::AbstractDict{T, T}, x) where {T <: MOI.Index}
+    map_indices(
+        variable_map::AbstractDict{T,T},
+        x::X,
+    )::X where {T<:MOI.Index,X}
 
 Shortcut for `map_indices(vi -> variable_map[vi], x)`.
 """
-function map_indices(variable_map::AbstractDict{T,T}, x) where {T<:MOI.Index}
+function map_indices(
+    variable_map::AbstractDict{T,T},
+    x::X,
+)::X where {T<:MOI.Index,X}
     return map_indices(vi -> variable_map[vi], x)
 end
 
diff --git a/src/Utilities/model.jl b/src/Utilities/model.jl
index 57e1a8014e..56a136cc73 100644
--- a/src/Utilities/model.jl
+++ b/src/Utilities/model.jl
@@ -485,7 +485,7 @@ end
 function MOI.get(
     model::AbstractModel,
     noc::MOI.NumberOfConstraints{F,S},
-) where {F,S}
+)::Int64 where {F,S}
     return MOI.get(model.constraints, noc)
 end
 
diff --git a/src/Utilities/struct_of_constraints.jl b/src/Utilities/struct_of_constraints.jl
index 20e48e811f..e70559bdea 100644
--- a/src/Utilities/struct_of_constraints.jl
+++ b/src/Utilities/struct_of_constraints.jl
@@ -117,7 +117,7 @@ end
 function MOI.get(
     model::StructOfConstraints,
     attr::MOI.NumberOfConstraints{F,S},
-) where {F,S}
+)::Int64 where {F,S}
     if !MOI.supports_constraint(model, F, S)
         return 0
     end
diff --git a/src/Utilities/universalfallback.jl b/src/Utilities/universalfallback.jl
index 00a3b56f17..bf55f26307 100644
--- a/src/Utilities/universalfallback.jl
+++ b/src/Utilities/universalfallback.jl
@@ -349,7 +349,7 @@ end
 function MOI.get(
     uf::UniversalFallback,
     attr::MOI.NumberOfConstraints{MOI.SingleVariable,S},
-) where {S}
+)::Int64 where {S}
     if MOI.supports_constraint(uf.model, MOI.SingleVariable, S)
         return MOI.get(uf.model, attr)
     elseif !haskey(uf.single_variable_constraints, S)
@@ -362,7 +362,7 @@ end
 function MOI.get(
     uf::UniversalFallback,
     attr::MOI.NumberOfConstraints{F,S},
-) where {F,S}
+)::Int64 where {F,S}
     return MOI.get(constraints(uf, F, S), attr)
 end
 
diff --git a/src/Utilities/vector_bounds.jl b/src/Utilities/vector_bounds.jl
index 4c7833fc8f..e6cc5a36b8 100644
--- a/src/Utilities/vector_bounds.jl
+++ b/src/Utilities/vector_bounds.jl
@@ -306,7 +306,7 @@ end
 function MOI.get(
     b::SingleVariableConstraints,
     ::MOI.NumberOfConstraints{MOI.SingleVariable,S},
-) where {S}
+)::Int64 where {S}
     flag = _single_variable_flag(S)
     return count(mask -> !iszero(flag & mask), b.set_mask)
 end
diff --git a/src/Utilities/vector_of_constraints.jl b/src/Utilities/vector_of_constraints.jl
index 3d8df22c01..293c76ef16 100644
--- a/src/Utilities/vector_of_constraints.jl
+++ b/src/Utilities/vector_of_constraints.jl
@@ -124,7 +124,7 @@ end
 function MOI.get(
     v::VectorOfConstraints{F,S},
     ::MOI.NumberOfConstraints{F,S},
-) where {F,S}
+)::Int64 where {F,S}
     return length(v.constraints)
 end
 
diff --git a/src/attributes.jl b/src/attributes.jl
index 0f3f6fa838..758dab5981 100644
--- a/src/attributes.jl
+++ b/src/attributes.jl
@@ -47,6 +47,19 @@ const AnyAttribute = Union{
 # embed it in a `Ref`
 Base.broadcastable(attribute::AnyAttribute) = Ref(attribute)
 
+"""
+    attribute_value_type(attr::AnyAttribute)
+
+Given an attribute `attr`, return the type of value expected by [`get`](@ref),
+or returned by [`set`](@ref).
+
+# Notes
+
+ * Only implement this if it make sense to do so. If un-implemented, the default
+   is `Any`.
+"""
+attribute_value_type(::AnyAttribute) = Any
+
 """
     struct UnsupportedAttribute{AttrType} <: UnsupportedError
         attr::AttrType
@@ -658,8 +671,11 @@ Returns a [`CallbackNodeStatusCode`](@ref) Enum.
 struct CallbackNodeStatus{CallbackDataType} <: AbstractOptimizerAttribute
     callback_data::CallbackDataType
 end
+
 is_set_by_optimize(::CallbackNodeStatus) = true
 
+attribute_value_type(::CallbackNodeStatus) = CallbackNodeStatusCode
+
 ## Optimizer attributes
 
 """
@@ -676,6 +692,8 @@ An optimizer attribute for the string identifying the solver/optimizer.
 """
 struct SolverName <: AbstractOptimizerAttribute end
 
+attribute_value_type(::SolverName) = String
+
 """
     Silent()
 
@@ -697,6 +715,8 @@ given.
 """
 struct Silent <: AbstractOptimizerAttribute end
 
+attribute_value_type(::Silent) = Bool
+
 """
     TimeLimitSec()
 
@@ -706,6 +726,8 @@ to `nothing`, it deactivates the solver time limit. The default value is
 """ # TODO add a test checking if the solver returns TIME_LIMIT status when the time limit is hit
 struct TimeLimitSec <: AbstractOptimizerAttribute end
 
+attribute_value_type(::TimeLimitSec) = Union{Nothing,Float64}
+
 """
     RawOptimizerAttribute(name::String)
 
@@ -724,6 +746,8 @@ integers. The default value is `nothing`.
 """
 struct NumberOfThreads <: AbstractOptimizerAttribute end
 
+attribute_value_type(::NumberOfThreads) = Union{Nothing,Int}
+
 ### Callbacks
 
 """
@@ -769,6 +793,8 @@ commonly called `callback_data`, that can be used for instance in
 """
 abstract type AbstractCallback <: AbstractModelAttribute end
 
+attribute_value_type(::AbstractCallback) = Function
+
 """
     LazyConstraintCallback() <: AbstractCallback
 
@@ -878,6 +904,10 @@ of `""` if not set`.
 """
 struct Name <: AbstractModelAttribute end
 
+attribute_value_type(::Name) = String
+
+@enum OptimizationSense MIN_SENSE MAX_SENSE FEASIBILITY_SENSE
+
 """
     ObjectiveSense()
 
@@ -887,7 +917,7 @@ must be an `OptimizationSense`: `MIN_SENSE`, `MAX_SENSE`, or
 """
 struct ObjectiveSense <: AbstractModelAttribute end
 
-@enum OptimizationSense MIN_SENSE MAX_SENSE FEASIBILITY_SENSE
+attribute_value_type(::ObjectiveSense) = OptimizationSense
 
 """
     NumberOfVariables()
@@ -896,6 +926,8 @@ A model attribute for the number of variables in the model.
 """
 struct NumberOfVariables <: AbstractModelAttribute end
 
+attribute_value_type(::NumberOfVariables) = Int64
+
 """
     ListOfVariableIndices()
 
@@ -921,6 +953,8 @@ A model attribute for the number of constraints of the type `F`-in-`S` present i
 """
 struct NumberOfConstraints{F,S} <: AbstractModelAttribute end
 
+attribute_value_type(::NumberOfConstraints) = Int64
+
 """
     ListOfConstraintTypesPresent()
 
@@ -942,6 +976,8 @@ it has non-integer coefficient and `F` is `ScalarAffineFunction{Int}`.
 """
 struct ObjectiveFunction{F<:AbstractScalarFunction} <: AbstractModelAttribute end
 
+attribute_value_type(::ObjectiveFunction{F}) where {F} = F
+
 """
     ObjectiveFunctionType()
 
@@ -960,6 +996,8 @@ attr = MOI.get(model, MOI.ObjectiveFunctionType())
 """
 struct ObjectiveFunctionType <: AbstractModelAttribute end
 
+attribute_value_type(::ObjectiveFunctionType) = Type{<:AbstractFunction}
+
 ## Optimizer attributes
 
 """
@@ -1001,6 +1039,8 @@ A model attribute for the final relative optimality gap, defined as ``\\frac{|b-
 """
 struct RelativeGap <: AbstractModelAttribute end
 
+attribute_value_type(::RelativeGap) = Float64
+
 """
     SolveTimeSec()
 
@@ -1008,6 +1048,8 @@ A model attribute for the total elapsed solution time (in seconds) as reported b
 """
 struct SolveTimeSec <: AbstractModelAttribute end
 
+attribute_value_type(::SolveTimeSec) = Float64
+
 @deprecate SolveTime SolveTimeSec
 
 """
@@ -1018,6 +1060,8 @@ In particular, for a mixed-integer program (MIP), the total simplex iterations f
 """
 struct SimplexIterations <: AbstractModelAttribute end
 
+attribute_value_type(::SimplexIterations) = Int64
+
 """
     BarrierIterations()
 
@@ -1025,6 +1069,8 @@ A model attribute for the cumulative number of barrier iterations while solving
 """
 struct BarrierIterations <: AbstractModelAttribute end
 
+attribute_value_type(::BarrierIterations) = Int64
+
 """
     NodeCount()
 
@@ -1032,6 +1078,8 @@ A model attribute for the total number of branch-and-bound nodes explored while
 """
 struct NodeCount <: AbstractModelAttribute end
 
+attribute_value_type(::NodeCount) = Int64
+
 """
     RawSolver()
 
@@ -1069,6 +1117,8 @@ results may be alternate certificates, or infeasible points.
 """
 struct ResultCount <: AbstractModelAttribute end
 
+attribute_value_type(::ResultCount) = Int
+
 """
     ConflictStatusCode
 
@@ -1098,6 +1148,8 @@ refiner stopped when computing the conflict.
 """
 struct ConflictStatus <: AbstractModelAttribute end
 
+attribute_value_type(::ConflictStatus) = ConflictStatusCode
+
 ## Variable attributes
 
 """
@@ -1119,6 +1171,8 @@ set`.
 """
 struct VariableName <: AbstractVariableAttribute end
 
+attribute_value_type(::VariableName) = String
+
 """
     VariablePrimalStart()
 
@@ -1199,6 +1253,8 @@ struct VariableBasisStatus <: AbstractVariableAttribute
     VariableBasisStatus(result_index::Int = 1) = new(result_index)
 end
 
+attribute_value_type(::VariableBasisStatus) = BasisStatusCode
+
 ## Constraint attributes
 
 """
@@ -1232,6 +1288,8 @@ You should _not_ implement `ConstraintName` for `SingleVariable` constraints.
 """
 struct ConstraintName <: AbstractConstraintAttribute end
 
+attribute_value_type(::ConstraintName) = String
+
 """
     SingleVariableConstraintNameError()
 
@@ -1325,6 +1383,8 @@ struct ConstraintBasisStatus <: AbstractConstraintAttribute
     ConstraintBasisStatus(result_index::Int = 1) = new(result_index)
 end
 
+attribute_value_type(::ConstraintBasisStatus) = BasisStatusCode
+
 function get_fallback(
     ::ModelLike,
     ::ConstraintBasisStatus,
@@ -1356,6 +1416,8 @@ then it returns the function stored internally instead of a copy.
 """
 struct CanonicalConstraintFunction <: AbstractConstraintAttribute end
 
+attribute_value_type(::CanonicalConstraintFunction) = AbstractFunction
+
 function get_fallback(
     model::ModelLike,
     ::CanonicalConstraintFunction,
@@ -1384,6 +1446,8 @@ It is guaranteed to be equivalent but not necessarily identical to the function
 """
 struct ConstraintFunction <: AbstractConstraintAttribute end
 
+attribute_value_type(::ConstraintFunction) = AbstractFunction
+
 function throw_set_error_fallback(
     ::ModelLike,
     attr::ConstraintFunction,
@@ -1415,6 +1479,8 @@ A constraint attribute for the `AbstractSet` object used to define the constrain
 """
 struct ConstraintSet <: AbstractConstraintAttribute end
 
+attribute_value_type(::ConstraintSet) = AbstractSet
+
 function throw_set_error_fallback(
     ::ModelLike,
     attr::ConstraintSet,
@@ -1468,13 +1534,11 @@ in the conflict. Its type is [`ConflictParticipationStatusCode`](@ref).
 """
 struct ConstraintConflictStatus <: AbstractConstraintAttribute end
 
-## Termination status
-"""
-    TerminationStatus()
+function attribute_value_type(::ConstraintConflictStatus)
+    return ConflictParticipationStatusCode
+end
 
-A model attribute for the `TerminationStatusCode` explaining why the optimizer stopped.
-"""
-struct TerminationStatus <: AbstractModelAttribute end
+## Termination status
 
 """
     TerminationStatusCode
@@ -1588,6 +1652,15 @@ This group of statuses means that something unexpected or problematic happened.
     OTHER_ERROR
 )
 
+"""
+    TerminationStatus()
+
+A model attribute for the `TerminationStatusCode` explaining why the optimizer stopped.
+"""
+struct TerminationStatus <: AbstractModelAttribute end
+
+attribute_value_type(::TerminationStatus) = TerminationStatusCode
+
 """
     RawStatusString()
 
@@ -1596,6 +1669,8 @@ stopped.
 """
 struct RawStatusString <: AbstractModelAttribute end
 
+attribute_value_type(::RawStatusString) = String
+
 ## Result status
 
 """
@@ -1659,6 +1734,8 @@ struct PrimalStatus <: AbstractModelAttribute
     PrimalStatus(result_index::Int = 1) = new(result_index)
 end
 
+attribute_value_type(::PrimalStatus) = ResultStatusCode
+
 """
     DualStatus(result_index::Int = 1)
 
@@ -1675,8 +1752,13 @@ struct DualStatus <: AbstractModelAttribute
     DualStatus(result_index::Int = 1) = new(result_index)
 end
 
+attribute_value_type(::DualStatus) = ResultStatusCode
+
 # Cost of bridging constrained variable in S
 struct VariableBridgingCost{S<:AbstractSet} <: AbstractModelAttribute end
+
+attribute_value_type(::VariableBridgingCost) = Float64
+
 function get_fallback(
     model::ModelLike,
     ::VariableBridgingCost{S},
@@ -1693,6 +1775,9 @@ end
 # Cost of bridging F-in-S constraints
 struct ConstraintBridgingCost{F<:AbstractFunction,S<:AbstractSet} <:
        AbstractModelAttribute end
+
+attribute_value_type(::ConstraintBridgingCost) = Float64
+
 function get_fallback(
     model::ModelLike,
     ::ConstraintBridgingCost{F,S},
diff --git a/test/attributes.jl b/test/attributes.jl
index c1d9983623..a75dfab24c 100644
--- a/test/attributes.jl
+++ b/test/attributes.jl
@@ -194,6 +194,21 @@ function test_UnsupportedSubmittable()
     )
 end
 
+function test_attribute_value_type()
+    @test MOI.attribute_value_type(MOI.CallbackNodeStatus(1)) ==
+          MOI.CallbackNodeStatusCode
+    @test MOI.attribute_value_type(MOI.LazyConstraintCallback()) == Function
+    @test MOI.attribute_value_type(MOI.RelativeGap()) == Float64
+    @test MOI.attribute_value_type(MOI.SimplexIterations()) == Int64
+    @test MOI.attribute_value_type(MOI.BarrierIterations()) == Int64
+    @test MOI.attribute_value_type(MOI.NodeCount()) == Int64
+    @test MOI.attribute_value_type(
+        MOI.ConstraintBridgingCost{MOI.SingleVariable,MOI.ZeroOne}(),
+    ) == Float64
+    @test MOI.attribute_value_type(MOI.VariableBridgingCost{MOI.ZeroOne}()) ==
+          Float64
+end
+
 function runtests()
     for name in names(@__MODULE__; all = true)
         if startswith("$name", "test_")